The present invention relates generally to the art of welding power supplies having high frequency (HF) arc starters and/or stabilizers. More specifically, it relates to a spark gap assembly used in producing a high frequency signal in a welding, cutting or induction power supply.
Arc welding is a process where the arc is often more difficult to start than to maintain. Also, in processes where the arc polarity periodically reverses, the arc is sometimes rectified (extinguished) during the polarity reversals. Accordingly, many prior art systems provide for arc starting and arc stabilizing.
One prior art arc starting and stabilization technique includes providing high voltage at a low current and a high frequency (RF e.g.), to start and stabilize (reignite on a half cycle basis) the arc because high frequency, low current, high voltage will not cause dangerous electrical shocks to the operator.
When high frequency is used only for starting it is called starting high frequency, and is disabled or not used after the arc has been started. Such systems often provide the high frequency voltage when the trigger on the welding torch is initially pulled until welding current is established. Systems which provide high frequency for arc stabilization may provide high frequency continuously, or on demandxe2x80x94i.e. only when the arc is rectified.
There are a variety of devices used to create the high frequency signal used for starting or stabilizing the arc. Typically, a spark gap is provided, and the high frequency signal is created by an arc periodically jumping the gap. When the gap is jumped, a sufficient burst of energy to start or stabilize the art is provided.
A spark gap is created by two electrical points being held a fixed distance apart. The assembly that holds the points in their proper position is called a spark gap assembly. A spark gap point, as used herein, includes the xe2x80x9cpointsxe2x80x9d or flat surfaces between which a spark arcs, preferably the head of a cylinder, but it can be other shapes and can include the entire cylindrical (or other shaped) body. A spark gap, as used herein, is the gap across which the spark arcs, and is between the points. A spark gap assembly can include the plastic housing, leads, points, screws and other fasteners which hold together or hold in place the housing.
One prior art spark gap assembly, available on the Miller Dynasty(trademark) welding power supply, included a plastic housing holding the electrical points. The points were cylindrically shaped and connected to a printed circuit board (pcb) by wire leads, one extending from each point and soldered to the circuit board. The position of the points, and thus the length of the gap their between, was adjusted by loosening a screw and then sliding a cylinder. While adequate, this prior art assembly had several drawbacks. First, it was relatively difficult to attach the spark gap points to the circuit boardxe2x80x94it required soldering, which can be a time-consuming procedure, and is prone to error. Also, the single piece used to form the spark gap housing was relatively expensive.
Another prior art design provided a housing with leads at the bottom of the housing, and held against the pcb, thus making contact. The position of the points, and thus the length of the gap their between, was adjusted by loosening a screw and then turning a cylinder, which was threaded. This prior art assembly has several drawbacks. First, it was not easy to adjust the gap distance because it required turning the threaded point after loosening several screws which clamped the points in position. Also, it was a relatively expensive housing to make.
Yet another prior art design provided two separate housings, each holding a point. A plurality of fins were provided on the housings to dissipate energy created when the spark jumped across the gap. The leads from each point were at the bottom of each housing, and held against the pcb, thus making contact. However, the gap was created by proper positioning of the two housings when they were mounted on the board, and thus mounting and proper gap sizing was a difficult task.
Accordingly, a spark gap assembly that is easily manufactured is desirable. Such an assembly preferably allows for easy adjustment of the gap, and for easy electrical connection to the pcb.
According to a first aspect of the invention a spark gap assembly for a welding power supply includes two conductive spark gap points, positioned to have a spark gap created therebetween. A non-conductive housing is made of two pieces of molded plastic that are clamped together. The housing has at least one receptacle for the spark gap points. Two leads, both conductive are disposed to electrically contact the spark gap points when they are in the receptacle. The leads further abut and electrically contact board leads when the assembly is mounted on a board.
The first and second pieces are substantially identical and, when assembled, abut one another along a surface generally extending in a first direction in one alternative.
Each housing piece defines half of each of two receptacles, and when the pieces are assembled, the halves of the receptacles mate to form the two receptacles, and the first and second receptacles have a generally cylindrical shape in other alternatives. Also, the two housing pieces, when assembled, may define a spark gap channel therethrough, and the spark gap channel is the receptacle.
Each lead is disposed about a portion of the periphery of a receptacle, and extends to the bottom of the assembly, and when assembled, the leads each have a bottom portion parallel to the bottom of the assembly, and the bottom portions include a cut-out disposed to have a fastener pass therethrough, to help fasten the assembly to the board in various alternatives.
The housing pieces each include at least one fastening hole extending in a direction generally perpendicular to the spark gap channel and a fastener extends through the fastening holes when the pieces are assembled, thus holding the first and second pieces in a clamped relationship in an alternative embodiment in other alternatives. The spark gap points are shaped to fit securely in the receptacles, such that when the pieces are clamped together the spark gap points are held securely in the receptacles. The leads extends receptacles, between the pieces, to the bottom of the assembly. The fastener may be a bolt and a nut.
The first and second piece each have at least one projection on the bottom, and each projection is received in one of a plurality of holes on the board, thereby positioning the first piece and the second piece, and/or the housing pieces define at least one hole therethrough, extending in a direction perpendicular to the bottom, to receive a fastener and to hold the assembly to the board in more alternatives.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.